As a sample analyzer for analyzing a sample to determine the amount of constituent contained therein, there has been widely used an automatic analyzer that emits light from a light source to a sample or a reaction mixture of a sample and a reagent; measures the amount of transmitted light of a single or a plurality of wavelengths obtained therefrom to calculate the absorbance; and determines the amount of constituent from the relation between the absorbance and the concentration according to the Beer-Lambert law (for example, see Patent Literature 1). The analyzer has a cell disk that repeats rotation and termination and a large number of cells holding a reaction mixture are arranged circumferentially thereon. During the cell disk rotation, a preset transmitted light measuring unit measures the change in absorbance over time for about ten minutes at a specific time interval.
The automatic analyzer includes a system for measuring the amount of transmitted light. The reaction of a reaction mixture is roughly divided into two types: an enzyme-substrate color reaction and an antigen-antibody agglutination reaction. The former is a biochemical analysis and includes LDH (lactate dehydrogenase), ALP (alkaline phosphatase), AST (aspartate aminotransferase), and the like as the test items. The latter is an immunoassay and includes CRP (C-reactive protein), IgG (immunoglobulin), RF (rheumatoid factor), and the like as the test items. The analyte to be measured by the latter immunoassay has a low blood level, and hence high sensitivity is required. Conventionally, high sensitivity has been provided by an immunological latex agglutination in such a manner that a reagent with an antibody sensitized (bound) to a latex particle surface is used; when a constituent contained in a sample is recognized and agglutinated, light is emitted to a reaction mixture; and then the mount of constituent contained in the sample is quantified by measuring the amount of light transmitted but not scattered by the latex aggregate.
Further, as the analyzer, an attempt has been made to increase sensitivity not by measuring the amount of transmitted light but by measuring the amount of scattered light. For example, there are disclosed a system that uses a diaphragm to separate the transmitted light and the scattered light and measure the absorbance and the scattered light at the same time (Patent Literature 2); a configuration in which precision is increased on a high concentration side by measuring the scattered light reflected by a large aggregate formed as a result of advanced agglutination reaction (Patent Literature 3); a method in which in front of and at the back of a reactor vessel, an integrating sphere is used to measure an average amount of light of each of the forward scattered light and the backward scattered light and correct turbidity changes due to cell dislocation (Patent Literature 4); a method of facilitating reduction in size and adjustment of the analyzer by arranging a fluorescent light—scattered light measurement detection system on the same plane as the direction of cell rotation (Patent Literature 5), and the like.